1. Field of the Invention
The present invention relates to providing an indication of the rate of flow of a fluid and particularly to the generation of a signal commensurate with a liquid flow rate in excess of a predetermined minimum. More specifically, this invention is directed to a flow detector and especially to an electrical device which will change state in response to a preselected rate of flow of a fluid in a conduit. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Brief Description of the Prior Art
Devices for producing an electrical signal which is commensurate with a preselected rate of flow of a fluid in a conduit are well known in the art and have utility in many diverse applications. For example, flow responsive devices for producing a control signal which is used to de-energize a pump when the flow rate falls below a preselected minimum are commonly employed in systems for transferring fluid between reservoirs. Examples of prior art flow responsive electrical signal generators are shown in U.S. Pat. Nos. 2,600,309; 3,140,606; 3,188,421; 3,559,197; and 3,857,277.
The prior art devices for generating an electrical signal in response to a rate of fluid flow have had one or more deficiencies. A principal one of these deficiencies has been a lack of versatility. Thus, the prior art devices were typically designed for use in a conduit of a single size and the "setpoint", i.e., the flow rate at which the device would change state and thus generate an information bearing signal, could not be varied. In the past, accordingly, a small pipe size flow detector would be used for low setpoints and, if the maximum flow rate which was expected was larger than the flow detector could handle, a larger device with an accordingly higher setpoint would be used. This, however, often produced the result that the setpoint of the larger flow detector could not be adjusted downwardly so as to enable the device to function properly in the smaller size conduit.
A further disadvantage of many prior art flow responsive signal generators resided in their susceptibility to contamination and particularly to sticking because of an accumulation, on a component of the device, of particulate matter entrained in the fluid flowing through the conduit in which the device was installed. The problem of faulty operation due to contamination has been particularly prevalent in flow detectors of the type where the entire flow in the conduit travels through the passage in which a moveable flow responsive element of the device is located.
Yet a further common problem with prior art flow responsive devices has resided in the fact that they have typically not been capable of adjustment in the field to permit "fine turning" to the actual flow conditions experienced.
Many prior art flow responsive signal generators have also unduly restricted flow in the conduit in which they have been installed, particularly when the flow rate is in excess of a minimum level of interest.